"Kate is such a style icon that even a few strands of grey would be a disaster, so I highly recommend that she cover it up," Clarke told a newspaper. "I hate grey hair."

The 33-year-old Duchess' greying hair was first scrutinised in 2013 and then again earlier this year during her second pregnancy with Princess Charlotte.

Clarke, who has worked with several royals including the late Princess Diana and Sarah Ferguson, Duchess of York, also claimed women cannot be seen to have grey, white or silver hair until they are "really old".

"Kate needs to get rid of her grey hair - it's not a good look," he said. "She does have amazing things done to her hair and it can look great, but unfortunately it's the case for women - all women - that until you're really old, you can't be seen to have any grey hairs.

"Men can go grey in their mid-50s and still be considered attractive - it's the whole silver fox thing - but it's not the same for women."

Clarke's comments have been widely ridiculed.

Among the chic, silver-haired women in the public eye is 35-year-old Sarah Harris, a fashion features director at Vogue magazine who began going grey as a teenager.

Sales of silver/grey hair dye are said to be booming, with pop star Rihanna and supermodel Jourdan Dunn among those in the public eye to test out the colour.

And the so-called 'Granny Hair' trend is proving popular on picture website Instagram.

It is thought around 25% of women in the UK and Ireland go grey before the age of 25. Broadcaster Pamela Ballantine (56) went grey as a teenager and is among the women in Northern Ireland to embrace their natural hair colour.